Since a substantial amount of coal combustion byproducts (CCB) are produced each year, generating value-added product from fly ash, which is a major constituent of these CCBs, has been an important area of research for several decades. Natural magnetite (NM), which is used to maintain dense medium slurry pulp density in coal preparation plants, has a current market value of more than $200 per ton. The use of fly ash derived magnetite (FAM) as an alternative to natural magnetite has potential benefits for dense medium processes, such as lower cost, greater stability at low medium density, more efficient delivery systems. This study developed a suitable processing scheme to extract high-grade (> 96%) magnetite from fly ash generated from burning high sulfur coal, and investigated the suitability of the FAM product for dense medium application in coal preparation plants. A classifying cyclone was utilized in the process flow sheet for the pre-concentration of FAM in its underflow stream, which was enriched to high grade FAM by a single stage wet magnetic separator of low intensity (~1000 gauss). A statistically designed experimental program was utilized to maximize the magnetite grade and recovery achieved from the above mentioned flow sheet. The FAM product particles had a slightly coarser particle size distribution than the NM particles. In addition, the FAM particles were found to have a spherical shape; but about one unit lower specific gravity in comparison to the NM particles. However, the F5 Stability Index of the resulting FAM product was found to be in the desired range of 30 to 40 for its suitable application as a dense medium. The coal cleaning performance obtained from a 0.15 m diameter dense medium cyclone using dense medium prepared from both of FAM and NM, were quite similar. However, the effective separation density (SG50) obtained from the FAM-based dense medium was significantly different from the medium density; this may need further investigation in future. A preliminary economic analysis, conducted for a hypothetical mini-plant having a fly ash handling capacity of 100 ton/hour, indicated the cost of FAM extraction to be nearly $5/ton. The cost assumes that the FAM extraction plant is located at the fly ash producing utility site and does not include the cost of thermal drying that may be required to reduce the moisture content of the FAM filter cake produced at the FAM plant. A preliminary civil engineering study conducted to investigate the effect of FAM extraction on the compressive strength property of the non-magnetic flyash (left behind after FAM extraction) failed to produce a conclusive finding. The specimens prepared using 10% and 30% fly ash replacements indicated that the compressive strength does not change due to FAM extraction. However, the specimens using 20% fly ash replacement indicated that compressive strength does change due to FAM extraction. Hence, a more detailed study is recommended to investigate this discrepancy.

Philosophiae Doctor - PhD / Coal fly ash has been studied extensively to understand the environmental impacts associated with its disposal, management and reuse. Although several beneficiation processes have been proposed, there has been little or no emphasis on the environmental safety of such processes, products and wastes. Elemental analysis has revealed that toxic elements and radionuclides are present in coal fly ash. Rare earth elements (REE) such as La, Ce and Y are also present in significant amounts in coal fly ash. The aims of this study were to determine the total elemental composition of coal fly ash using different analytical techniques; to validate the application potentials of fly ash beneficiation processes in terms of their environmental safety; and to valorise coal fly ash with a view of recovering REE either by concentrating or leaching the REE in the coal fly ash, products or waste from the beneficiation processes. The beneficiation processes studied were treatment of acid mine drainage (AMD) with fly ash; and the synthesis of geopolymer from fly ash. The fresh fly ash sample used in this study was collected directly from the hoppers at Matla power station and the AMD sample was collected from Carletonville goldmine. A total of 54 major, trace and REE were accurately determined in the ash using different analytical techniques. It was shown that the elemental content of Matla fly ash was of the same order as the SRM NIST coal fly ash 1633b. The comparative study of the four analytical techniques established that ENAA can accurately determine the major, minor and trace elements; that XRF is best suited for the determination of the major and minor elements, whilst the LA ICP-MS is reliable for trace elements determination. The solid residue (AMD/FA) resulting from the AMD interaction with fly ash was characterized with fly ash and the results compared. The results revealed that the amounts of La (141.09 ± 3.85 mg/kg), Ce (27.45 ± 2.04 mg/kg), and Nd (63.73 ± 0.05 mg/kg) in AMD/FA residue was considerably higher than their average abundance in the earth crust that varies from 66 mg/kg in Ce and 40 mg/kg in Nd to 35 mg/kg in La. The results also showed that the AMD/FA residue contained As (11.39 ± 1.21 mg/kg), Cd (3.77 ± 0.02 mg/kg), Cr (72.43 ± 1.27 mg/kg), Hg (10.50 ± 0.85 mg/kg), Ni (124.15 ± 1.6 mg/kg) and Pb (22.46 ± 1.43 mg/kg) which are potentially harmful if leached in to the environment in excessive amounts.

Coal fly ash is a by-product of coal combustion that has drawn renewed public scrutiny due to the negative environmental impacts from accidental release of this waste material from storage facilities. Historically, the leaching of toxic elements from coal fly ash into the environment has always been a major environmental concern. Despite extensive efforts into the characterization of coal fly ash, effective models for the fate and transport of toxic fly ash constituents have remained lacking, making it difficult to perform accurate environmental impact assessment for coal fly ash. To close this critical knowledge gap, the overall objective of this study was to develop a predictive model for the leaching of toxic elements from fly ash particles. First, physical properties of coal fly ash were characterized to evaluate their contribution to elemental transport. Unburned carbon was shown to contribute to the sorption of arsenic to fly ash, which slowed the release of arsenic from fly ash. In parallel, leaching properties of various elements were determined to differentiate species of varying leaching capacities, demonstrating that the majority of toxic elements were not mobile under environmentally relevant conditions. Subsequently, a mechanistic model for the dissolution of fly ash elements was developed and validated with batch kinetics studies. Furthermore, elemental dissolution was integrated with hydrodynamic modeling to describe the leaching of toxic elements from fly ash in dry disposal facilities, which was validated by column studies. The mechanistic model developed and validated in this research represents the first such model that successfully characterized the complex processes underlying the release and transport of toxic elements in coal fly ash, providing a valuable tool to predict the environment impact of coal fly ash and develop more effective management practices for both the industry and regulators.

Thirty million tons of coal fly ash are produced each year in South Africa of which approximately 5% is utilised beneficially. With the growing concern about pollution and increasing landfill costs, the study of the utilisation and application of coal fly ash has increased worldwide. The morphology and particle size of fly ash make it suitable for application as filler in polymers, but its application is hindered by the lack of compatibility between the inorganic surface of the ash and the organic matrix of the polymer. Another concern is the agglomeration between fly ash particles. For this reasons, surface treatment is usually performed on mineral fillers to enhance workability and compatibility between the polymer and filler. This study involved the surface modification of South African coal fly ash with an anionic surfactant, sodium lauryl sulphate (SLS), under different treatment conditions. Surface and physical properties of the untreated and treated fly ash were studied systematically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in order to determine the extent of interaction between the SLS and the fly ash surface. Other analytical techniques applied include Thermogravimetric analysis (TGA-FTIR), Particle size distribution, X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF), Raman spectroscopy and Fourier Transform Infrared spectroscopy FTIR). Although the overall chemical composition of the SLS modified coal fly ash investigated in this study was not altered extensively, significant changes could be observed in its physical properties. The hydrophilic surface of untreated fly ash was rendered hydrophobic after SLS treatment. SEM results indicated a decrease in agglomeration between fly ash spheres upon surfactant treatment, while results obtained from TEM have shown agglomerates on the surface of most of the fly ash spheres. There is a distinct difference between the morphology of agglomerates on the untreated and SLS modified fly ash, and also between samples treated under different conditions. Not all SLS modified fly ash particles were covered with agglomerates to the same degree. Results obtained from FTIR and TGA-FTIR studies were promising in the sense that hydrocarbon fractions could be observed in the TGA-FTIR decomposition products. The possibility of interactions between fly ash and SLS could be deduced from the FTIR results of the solid samples, due to a small shift in peak positions of the S-O stretch vibration, which may be indicative of electrostatic interactions rather than bonding interactions between SLS and fly ash. The presence of SLS could not be confirmed by Raman spectroscopy, but rendered information about the spatial distribution of the various phases in the fly ash. Feasibility tests were performed on the application of fly ash samples as filler in PVC. These results indicate that SLS treated fly ash can successfully replace CaCO3 as filler in PVC under conditions of low filler loadings / Dissertation (MSc)--University of Pretoria, 2013. / Chemistry / unrestricted

Philosophiae Doctor - PhD / Zeolites are widely used as environmentally friendly solid catalysts or catalyst supports in the refining and petrochemical industries. ZSM-5 zeolite is composed of a three-dimensional medium pore structure (openings of 5-5.5 Å) with high silica content, high temperature stability and strong acidity making it a well-known and an established catalyst for several petroleum derived chemical processes such as cracking, aromatic alkylation, disproportionation, Methanol-to-Gasoline, isomerisation, etc. Nowadays, the synthesis of ZSM-5 zeolite from silica, alumina sources and structure directing agents (templates) is well known. Its synthesis is possible from fly ash, which is a low cost source of both silica and alumina. Fly ash is an inorganic residue resulting from the combustion of coal in electricity generating plants, consisting mostly of SiO₂ and Al₂O₃. ZSM-5 zeolite has not been synthesised from South African coal fly ash and the literature reports that fly ash-based ZSM-5 zeolite was synthesised only with tetrapropylammonium (TPA+) as structure directing agent and required an excessive amount of additional silica. The final ZSM-5 product was reported to still contain fly ash mineral phases after synthesis. This prevents the use of fly ash as a ZSM-5 zeolite precursor. Moreover, the synthesis of a high purity ZSM-5 zeolite from fly ash without additional silica has not been yet reported. This study aimed to synthesise high purity ZSM-5 zeolite from South African coal fly ash without additional silica, and with tetrapropylammonium bromide (TPABr), 1,6- hexanediamine (HDA) or 1-propylamine (PA) as structure directing agent. This aim was achieved by first optimising the synthesis of ZSM-5 zeolite from South African coal fly ash based on a formulation reported in the literature with fumed silica and TPABr as additional source of silica and structure directing agent respectively. Thereafter, the obtained optimum conditions were used to synthesise other fly ash-based ZSM-5 zeolite products by substituting TPABr with HDA or PA. Two routes of treating the as-received fly ash prior to the hydrothermal synthesis were applied in order to improve the quality of the final products or reduce the amount of the fumed silica that was used. The first route consisted of treating the as-received fly ash with concentrated H₂SO₄ in order to remove a certain amount of aluminium and increase the Si/Al in the acid treated fly ash solid residue but also remove some other elements such as Fe, Ca, Mg, and Ti which might have an undesirable effect on the product quality. The acid treated fly ash solid residue was used as ZSM-5 precursor with fumed silica as additional silica source and TPABr, HDA or PA as structure directing agent. The ZSM-5 zeolite products that were synthesised from the as-received fly ash as well as from the H₂SO₄ treated fly ash were treated with oxalic acid solution in order to reduce the aluminium content in the final products. The second route consisted of fusing the as-received fly ash with NaOH and treating the powder fused fly ash extract with oxalic acid solution. The obtained fused and oxalic acid treated fly ash extracts were used as ZSM-5 precursors without additional fumed silica and with TPABr, HDA or PA as structure directing agent. ZSM-5 zeolite was synthesised from the as-received South African coal fly ash not only with the commonly used structure directing agent TPABr but also with two other, lower cost structure directing agents, HDA and PA. The synthesis process did not generate any solid waste as fly ash was used as bulk, which could be a way of valorising South African coal fly ash. However, the final products contained some fly ash mineral phases such as mullite and quartz, and had poor physical and chemical properties compared to a commercial H-ZSM-5 zeolite. The treatment of the as-received fly ash with H₂SO4 resulted in fly ash-based ZSM-5 zeolite products with better physical and chemical properties than those of ZSM-5 zeolite products that were synthesised from the as-received fly ash. Moreover, the post-synthesis treatment of the fly ash-based ZSM-5 zeolite products with oxalic acid resulted in an increase in the Si/Al ratio, offering a post-synthesis route to adjust the acidity of the catalysts. However, mullite and quartz phases were still present in the synthesised products. Alternatively, high purity ZSM-5 zeolite was synthesised from the fused and oxalic treated fly ash extracts without additional silica and with TPABr, HDA or PA as structure directing agent. Moreover, these synthesised fly ash-based ZSM-5 zeolite products had similar physical and chemical properties to the commercial H-ZSM-5 zeolite. The synthesised fly ash-based ZSM-5 zeolite products were used as solid catalysts in the Methanol-to-Olefins (MTO) and Nazarov reactions. The ZSM-5 zeolite products that were synthesised from the H₂SO4 treated fly ash as well as fused and oxalic treated fly ash were successfully used as solid catalysts in the MTO and Nazarov reactions. The ZSM-5 zeolite products that were synthesised from the H₂SO₄ treated fly ash presented a similar trend in MTO and Nazarov reactions depending on the structure directing agent that was used, and the ZSM-5 zeolite that was synthesised with HDA as structure directing agent had the highest MTO and Nazarov conversion. However these catalysts deactivated more quickly compared to the commercial H-ZSM-5 zeolite. On the other hand, the zeolites that were synthesised from the fused and oxalic acid treated fly ash had a high initial MTO conversion equivalent to the commercial H-ZSM-5 zeolite. However, they deactivated after 5 h of time on stream due to diffusional constraints, because of their large crystal sizes. This study developed novel routes in the synthesis of high value zeolites from fly ash. ZSM-5 zeolite was synthesised from fly ash with structure directing agents other that TPA+ cation and had acceptable Brønsted acidity and high initial conversion in MTO and Nazarov reactions. This has not been yet reported in the literature. Moreover, for the first time a high purity ZSM-5 zeolite was synthesised from fly ash without additional silica and had similar properties to a commercial H-ZSM-5 zeolite. This constituted a breakthrough in the fly ash-based ZSM-5 zeolite synthesis procedure, which will promote the valorisation of fly ash through ZSM-5 synthesis due to avoiding the addition of silica source in the hydrothermal gel and preventing the presence of fly ash mineral phases in the final products. This study can have a significant economic and environmental impact in South Africa if the synthesis process is scaled up as it provides a potentially cheap and innovative way of using waste for making a high value green and acid catalyst, namely ZSM-5 zeolite that has several catalytic applications; and it promotes the valorisation of South African coal fly ash that is considered by many as waste material. / National Research Foundation (NRF)

>Magister Scientiae - MSc / Coal is seen as a reliable and secure energy source in many countries around the world despite the development of a number of alternative sources of energy. A rise in global energy demand has led to an increase in coal consumption. Consequently, global coal fly ash (CFA) production has increased creating a pressing need for recycling and utilisation of coal fly ash. South Africa produces 50 million tons of ash per year from coal combustion with only about 10 % being utilised. There has been a rise in demand for REEs over the past decades due to their use in optics, automotive, electronics, energy, defence industries etc. These precious elements are known to be contained in CFA, making it a potential source.

>Magister Scientiae - MSc / There has been increasing interest in finding alternative sources for Rare Earth Elements (REEs) due to their application in green energy and Coal Fly Ash (CFA) has been found to be a viable potential source. Thus investigations on the feasibility of recovering REEs from CFA and the possibility of optimizing the current recovery techniques have become popular. The main focus in the investigations has been to use equipment and products that are environmentally sustainable and economically efficient. In addition, studies have shown that there is a relationship between the particle size of CFA and the REE concentration, which can potentially increase the recovery of REEs. However, there have been inconsistencies in the findings of this relationship.

Masters of Science / Eskom supplies to 95% of South Africa’s energy needs and it primarily comes from coal combustion at their coal–fired power stations. Large volumes of fly ash are generated at these coal-fired power stations as a by-product of the coal combustion process. Fly ash is disposed onto landfills at the respective power stations and these landfills are currently running out of storage space. Subsequently, there are concerning environmental impacts upon the natural water environment resulting from coal mining. More specifically, the discharge of acid mine (AMD) water from historical coal mines impact negatively on the water quality in the nearby rivers and dams in the Witbank area. Therefore, as a consequence of the limited space at fly ash landfills, Eskom has embarked on finding alternative ways to re-use fly ash in different applications such as: soil amelioration and land reclamation, road construction as well as brick and cement development. This study focussed on the feasibility of disposing fly ash into the backfill of historical and future coal mines with the intention to firstly reduce fly ash disposal at existing landfills and secondly to improve the decant water quality of the coal mines in the Witbank area. Globally, fly ash has been successfully used in mine backfilling and AMD treatment in countries such as United States of America and India, due to cementitious properties of their fly ash. However, there is limited knowledge on how South African fly ash would behave under backfilled conditions of opencast coal mines where it will be exposed to acidic water environments. This is due to the fact that South African fly ash is considered a Level 3 type hazardous waste, due to its heavy metal concentrations. This waste classification is unique and the strictest compared to global classifications and these methodologies specify that fly ash should be disposed onto lined waste disposal sites due to the potential leaching of heavy metals from these waste sites. It is important to understand the hydrogeological and hydro-geochemical properties of fly ash over time once it is exposed to acid mine water. Field and laboratory tests were conducted to understand these hydrogeological and hydro-geochemical properties of fly ash. Falling head hydraulic tests were conducted at two existing ash landfill sites to determine the hydraulic conductivity (K) of ash of different age. The results exhibit a decreasing trend in K with increasing age. This is due to the pozzolanic nature of fly ash and secondary mineralization of gypsum which causes the fly ash to harden in the presence of water from irrigation for dust suppression together with precipitation over time. Laboratory testing included the use of constant head Darcy column tests to determine the change in K and geochemical properties of the leachate over time. Natural AMD with a pH of 2.5 and a metal composition was used as influent and the leachate were routinely collected and analysed for metal concentrations. The hydraulic conductivity of the fly ash showed a decreasing trend over time. During the placement of coal ash, the moisture allows pozzolanic reactions to solidify the coal ash and lowers the K, towards 10-1 m/d, relative to fresh ash. Secondary mineralization of calcium minerals, in the coal ash contributes to a further decrease in the K, by another order of magnitude from 10-1 m/d towards 10-2 m/d. Sulphate and iron minerals from the AMD also played a major role in the decreasing K as they accumulate in void spaces and having a clogging effect, decreasing the K to 10-3 m/d. The alkaline nature of the coal ash initially neutralizes the acidic levels of AMD from an inflow pH = 2.5 to an outflow pH = 11. Acidification of the outflow towards a pH = 4 was observed, due to large volumes of AMD (>80 000 mL) flowing through short coal ash columns. The K decreased to 3 orders of magnitude, from an initial 10-1 m/d to 10-3 m/d, with the AMD iron (>150 mg/L) and sulphate concentration (>2000 mg/L) playing the dominant role in reducing the hydraulic conductivity. From the geochemical leach test results, it was observed that most of the leachate water was of a better quality than the influent AMD water quality. The outflow pH (pH = 11 to pH = 4) was higher than the pH of the inflow AMD (pH = 2.5). Overall EC reduced in discharge compared to inflow AMD (ECinflow: 535 – 545 mS/m versus ECoutflow: 350 – 490 mS/m), although Na and K in the leachate exhibited higher concentrations (10+2 mg/L) compared to the AMD inflow concentrations (10+1 mg/L). However, most of the other chemical elemental concentrations such as Fe (10-2 – 10+1 mg/L), Si (10-2 – 100 mg/L), Al (10-2 – 10+1 mg/L), Mn (10-2 – 10+1 mg/L), Cr (10-3 – 100 g/L) and SO4 (10+2 – 1+3 mg/L) in the discharge showed lower concentrations when compared to the inflow Fe (10+2 mg/L), Si (100 mg/L), Al (10+1 mg/L), Mn (10+1 mg/L), Cr (10-2 mg/L) and SO4 (10+3 mg/L) concentrations. These results show how fly ash backfill may impact on the current coal mining environment. Overall, the laboratory hydraulic conductivity and geochemical testing showed promising results for fly ash backfilling. Based on this research, fly ash can be used to alter the existing coal mining environment as it is currently known in the Witbank area. The topography, hydraulic conductivity and the water table within the backfill can be altered to improve decant water quality of ash backfilled coal mines.

As indústrias lançam diversos poluentes no meio ambiente. Dentre os poluentes destacam-se os elementos tóxicos presentes em efluentes líquidos por acarretarem alto risco potencial à saúde humana e ao meio ambiente. Os efluentes podem ser tratados por materiais adsorventes, os quais podem ser provindos de resíduos industriais. Uma forma de contribuir significativamente na sustentabilidade de uma indústria é a transformação de um de seus resíduos em sub-produto de valor agregado para aplicação no tratamento de seus efluentes líquidos como adsorvente de baixo custo. O objetivo deste trabalho foi sintetizar, e caracterizar zeólitas de cinzas de carvão e avaliar sua aplicação como material adsorvente no tratamento de efluente. Os materiais zeolíticos derivados de três tipos diferentes de cinzas de carvão (cinzas manga, cinzas ciclone e cinzas pesadas) geradas na usina termelétrica de Figueira-PR foram usados para tratar o lixiviado do aterro de cinzas de carvão da mesma usina. As seguintes características das zeólitas foram determinadas: composição mineralógica, composição química, teor de carbono total, análise morfológica, área superficial específica, capacidade de troca catiônica (CTC), perda ao fogo, pH, condutividade e densidade aparente. A fase zeolítica formada foi do tipo sodalita com as três amostras usadas como matéria prima após ativação hidrotérmica alcalina. O material zeolítico de cinzas manga apresentou a menor relação SiO2/Al2O3 (1,46), maior CTC (2,36 meq g-1) e área superficial específica (69,5 m2 g-1) e, consequentemente, maior capacidade de remoção dos íons do efluente. As concentrações de As e Cr estavam acima do padrão de lançamento de efluentes. As três amostras de materiais zeolíticos apresentaram uma remoção significativa de Ni, Cd, Zn e Co na dose de 10 g.L-1. Os materiais zeolíticos das cinzas manga e ciclone foram eficientes para reduzir a concentração de As abaixo do limite imposto pela legislação, enquanto a remoção do Cr não foi efetiva com nenhum dos materiais. Na segunda etapa do trabalho, as zeólitas foram modificadas com o surfactante brometo de hexadeciltrimetilamônio (HTDMA-Br) em concentrações de 1,8 e 20 mmol L-1. A modificação das zeólitas não melhorou a eficiência de remoção do As. A remoção do Cr usando a amostra de zeólita de cinzas manga modificada com HDTMA-Br 20 mmol L-1 resultou em uma concentração final muito próxima ao limite permitido pela legislação. / The industries release various types of pollutants into to the environment. Among these pollutants are the liquid effluents containing toxic elements, they carry a high potential risk to human health and the environment. Some effluents can be treated by adsorbent materials, which can be made from industrial waste. One way to contribute significantly to the sustainability of an industry is to transform one of its residues into a value-added by-product and use in the treatment of its own liquid effluents as a low cost adsorbent. The objective of this estudy was to synthesize and characterize coal ash zeolites and evaluate their application as adsorbent material in the treatment of effluent. Zeolite materials derived from three different types of coal ash (fly ashes, cyclone ashes and heavy ashes) generated at the Figueira-PR thermoelectric plant were used to treat leachate from the coal ash landfill of the same plant. The following zeolite characteristics were determined: mineralogical composition, chemical composition, total carbon content, morphological analysis, specific surface area, cation exchange capacity (CTC), fire loss, pH, conductivity and bulk density. The zeolite phase formed with the three samples used as raw material after alkaline hydrothermal activation was sodalite. The zeolite material from fly ash had the lowest SiO2/Al2O3 ratio (1.46), higher CTC (2.36 meq g-1) and specific surface area (69.5 m2 g-1) and, consequently, greater effluent removal capacity. The As and Cr concentrations were above the effluent discharge standard. The three samples of zeolitic materials showed a significant removal of Ni, Cd, Zn and Co in the dose of 10 g L-1. The zeolite materials from fly and cyclone ash were efficient to reduce As concentrations below the limit imposed by legislation, while removal of Cr was not effective with any of the materials. In the second stage of the study, the zeolites were modified with the surfactant hexadecyltrimethylammonium bromide (HTDMA-Br) in concentrations of 1.8 and 20 mmol.L-1. The zeolite removal efficiency of As did not improve after its modification. Removal of Cr using the 20 mmol.L-1 modified HDTMA-Br modified fly ash zeolite sample resulted in a final concentration very close to the limit allowed by the legislation.

No presente estudo obteve-se com sucesso o compósito zeólita:magnetita usando-se como material de partida sulfato ferroso para síntese da magnetita e cinzas leves de carvão para síntese da fase zeolítica. A zeólita foi sintetizada por tratamento hidrotérmico alcalino e as nanopartículas de magnetita foram obtidas pela precipitação de íons Fe2+ em uma solução alcalina. Uma reprodutibilidade foi alcançada na preparação de diferentes amostras do nanocompósito zeolítico. O material foi caracterizado pelas técnicas de espectrometria de Infravermelho, difratometria de raios-X de pó, fluorescência de raios-X, microscopia eletrônica de varredura com a técnica de EDS, massa especifícia e área específica e por outras propriedades físico-químicas. O compósito era constituído pelas fases zeolíticas hidroxisodalita e NaP1, magnetita, quartzo e mulita das cinzas remanescentes do tratamento alcalino e magnetita incorporada na sua estrutura. A capacidade de remoção de U(VI) de soluções aquosas sobre o compósito zeólita:magnetita foi avaliada pela técnica descontínua. Os efeitos do tempo de contato e da concentração inicial do adsorbato sobre a adsorção foram avaliados. Determinou-se o tempo de equilíbrio do sistema e foram avaliados os modelos cinéticos de pseudo-primeira ordem, pseudo-segunda ordem e o modelo de difusão intrapartícula. Um tempo de contato de 120 min foi suficiente para a adsorção do íon uranilo alcançar o equilíbrio. A velocidade de adsorção seguiu o modelo cinético de pseudo-segunda-ordem, sendo que a difusão intrapartícula não era a etapa determinante do processo. Dois modelos de isotermas de adsorção, os modelos de Langmuir e de Freundlich, também foram avaliados. O modelo de Langmuir foi o que melhor se ajustou aos dados experimentais. A partir do modelo cinético e da isoterma que melhor descreveram o comportamento do sistema foi possível calcular os valores teóricos para a capacidade máxima de adsorção do U(VI) sobre o compósito zeólita:magnetita. As capacidades máximas de remoção calculadas foram de 20,7 mg.g-1 pela isoterma de Langmuir e de 23,4 mg.g-1 pelo modelo cinético de pseudo-segunda ordem. O valor experimental obtido foi 23,3 mg.g-1. / Within this work, a magnetic-zeolite composite was successfully synthesized using ferrous sulfate as raw material for the magnetic part of the composite, magnetite, and coal fly ash as raw material for the zeolitic phase. The synthesis of the zeolitic phase was made by alkali hydrothermal treatment and the magnetite nanoparticles were obtained through Fe2+ precipitation on alkali medium. The synthetic process was repeated many times and showed good reproducibility comparing the zeolitic nanocomposite from different batches. The final product was characterized using infrared spectroscopy, powder X-ray difraction, X-ray fluorescence, scanning electron microscopy with coupled EDS. Specific mass, specific surface area and other physicochemical proprieties. The main crystaline phases found in the final product were magnetite, zeolites types NaP1 and hydroxysodalite, quartz and mulite, those last two remaing from the raw materials. Uranium removal capacity of the magnetic zeolite composite was tested using bathc techniques. The effects of contact time and initial concentration of the adsorbate over the adsorption process were evaluated. Equilibrium time was resolved and the following kinectics and difusion models were evaluated: pseudo-first order kinectic model, pseudo-second order kinectic model and intraparticule difusion model. A contact time of 120 min turned out to be enough to reach equilibrium of the adsorption process. The rate of adsorption followed the pseudo-second order model and the intraparticle diffusion didnt turned out to be a speed determinant step. Two adsorption isotherms models, the Langmuir model and the Freundlich model, were also evaluated. The Langmuir model was the best fit for the obtained experimental data. Using the best fitted adsorption isotherm and kinectic model, the theorical maximum adsorption capacity of uranium over the composite was determined for both models. The maximum removal capacity calculated was 20.7 mg.g-1 for the Langmuir isotherm and 23.4 mg.g-1 for the pseudo-second order model. The experimental value attained was 23,3 mg.g-1.